Constant light intensity servo control unit

ABSTRACT

The present disclosure relates to devices for controlling the light intensity of a lamp, automatically, under unfavorable conditions. Electronic servocontrol circuits have been used to maintain associated circuit elements within certain operational limits. The disclosed invention, while generally being of this type, presents a rugged, compact, servocontrol unit designed to regulate the output of a storage battery to ensure a particular light intensity of a lamp contained in a pressure-resistant housing. Precise light intensity regulation, to a degree far in excess of that discernible by the human eye, is necessary where a lamp provides a source of illumination for a remotely located nephelometer, an instrument for determining the concentration or particle size of suspensions by means of transmitted or reflected light. Such precise light intensity regulation is achieved by a serially connected control unit formed of a pair of parallel power transistors controlled by a first and a second feedback loop coupled to their bases. The first feedback loop compares a desired potential provided by a Zener diode to the output of the control unit and develops a first control signal that functions to change the bias on the two parallel transistors until the output of the control unit substantially equals the desired potential. A second feedback loop, having a photocell positioned to receive impinging radiation from the lamp, produces an output signal indicative of the lamp&#39;&#39;s radiation intensity. A predetermined lamp intensity, causing the photocell to give a predetermined resultant signal, causes no current feedback to the control unit. A resultant signal caused by a deviation from the predetermined lamp intensity results in the creation and the transfer of a second signal to the control unit and consequent regulation of the lamp&#39;&#39;s intensity. Thus, a circuit ensuring internal potential regulation, as well as regulation of a lamp&#39;&#39;s intensity caused by deterioration of the lamp&#39;&#39;s elements, provides more stable and precise light intensity regulation than contemporary circuits.

United States Patent [72] Inventor Robert L. Seeley San Diego, Calif.[21] Appl. No. 780,942 [22] Filed Nov. 29, 1968 [45] Patented Jan. 26,1971 [73] Assignee the United States of America as represented by theSecretary of the Navy [54] CONSTANT LIGHT INTENSITY SERVO CONTROL UNIT 2Claims, 2 Drawing Figs.

52 us. Cl 259 295 315/151; 323/20, 3 23/21 [51] Int. Cl G05d 25/00,G05f1/56, H05b 41/392 [50] Field of Search 315/151; 250/205; 317/20, 21

[56] References Cited UNITED STATES PATENTS 3,031,578 4/1962 Colburn250/205 3,358,217 12/1967 Deelman 315/15IX 3,431,464 4/1969 Brischink315/151X 3,456,155 7/1969 Buchanan 3l5/151X 3,473,084 1/1969 Dodge315/151X Primary ExaminerRoy Lake Assistant Examiner-C. R. CampbellA!!0rneys-R. S. Sciascia, E. F. Johnston and T. G. Keough ABSTRACT: Thepresent disclosure relates to devices for controlling the lightintensity of a lamp, automatically, under unfavorable conditions.Electronic servocontrol circuits have been used to maintain associatedcircuit elements within certain operational limits. The disclosedinvention, while generally being of this type, presents a rugged,compact, servocontrol unit designed to regulate the output of a storagebattery to ensure a particular light intensity of a lamp contained in apressure-resistant housing. Precise light intensity regulation, to adegree far in excess of that discernible by the human eye, is necessarywhere a lamp provides a source of illumination for a remotely locatednephelometer, an instrument for determining the concentration orparticle size of suspensions by means of transmitted or reflected light.Such precise light intensity regulation is achieved by a seriallyconnected control unit formed of a pair of parallel power transistorscontrolled by a first and a second feedback loop coupled to their bases.The first feedback loop compares a desired potential provided by a Zenerdiode to the output of the control unit and develops a first controlsignal that functions to change the bias on the two parallel transistorsuntil the output of the control unit substantially equals the desiredpotential. A second feedback loop, having a photocell positioned toreceive impinging radiation from the lamp, produces an output signalindicative of the lamps radiation intensity. A predetermined lampintensity, causing the photocell to give a predetermined resultantsignal, causes no current feedback to the control unit. A resultantsignal caused by a deviation from the predetermined lamp intensityresults in the creation and the transfer of a second signal to thecontrol unit and consequent regulation of the lamps intensity. Thus, acircuit ensuring internal potential regulation, as well as regulation ofa lamps intensity caused by deterioration of the lamps elements,provides more stable and precise light intensity regulation thancontemporary circuits.

CONSTANT INTENSITY /9 INTENSITY SAMPLER y INVERTING AMPLIFIER sissslaszSAMPLER v94 ADDER COMPARATOR VOLTAGE VOLTAGE STANDARD CURRENT ADDERINVENTOR. ROBERT L. SEE'LEY SOURCE PATE 'NTE D m6 |97| CURRENT IONSTANTLIGHT INTENSITY SERVO CONTROL UNIT BACKGROUND OF THE INVENTION Theinventionis adapted specifically, but not exclusively, for deep seaoperations requiring a self-contained housing enclosing a power voltagesource, regulating circuitry, and a lamp, all remotely located fromsupervisory control circuitry for providing a highly stable source oflight at a given light intensity. Heretofore such light intensity, used.with undersea photography or for scientific measurements, has beenprovided by placing a photocell in the radiation path of a source oflight and noting changing variations in the radiant light on a connectedammeter, that is to say, as the intensity of the light varied, thereading on the ammeter varied. An operator, upon observing the ammetersfluctuation,'would change the setting of a potentiometer connected inseries with a source of potential and the lamp to bring the intensity ofthe light back to the desired level, At great depths pressures usuallyprohibit first hand observation, or, if a pressurized habitat wereavailable to protect an observer from the crushing pressures, electricalconnections permitting adjustment of the light intensity unit mustpierce the shell of the habitat, thereby greatly weakening itsstructural strength and greatly increasing its cost. In additiori to theaforementioned disadvantages, an externally located photocell would besusceptible to damage and may incorrectly give readings representativeof light intensity due to water cloudiness between the cell and themonitored lamp. All the present voltage regulation systems fail toprovide a compact, two-feedback loop voltage regulation systems fail topro vide a compact, two circuit, including a hermetically sealedphotocell and serially connected power transistors mounted on aheat sinkfor regulating an interconnected lamp coupled to asource of potential. i

SUMMARY OF THE INVENTION -,The present invention is directed toproviding an apparatus for controlling the light intensity of a lamp andincludes a control unit-having a pair of parallel-connectedtransistorsforming an adjustable impedance, serially'connecting a source ofpotential to a lamp. A first aid and a second feedback circuit monitorthe output from the control unit to respectively provide a coarsecontrol signal yielding a desired potential and a fine control signalfor precisely adjusting the radiation intensi- 'ty of the lamp. -Byadding the. coarse and fine control signals and feeding the addedsignals to the control unit, such desired light intensity is achieved.

It is a prime object of the instant invention to provide a lampintensity regulation circuitpermitting superior regulation as comparedto contemporary circuits.

- Another object of the instant invention is to provide a circuitpermitting precise lamp intensity regulation requiring no outsidesupervision ormanipulation.

Yet another object is to provide a compact regulation circuit adapted tooperate under severe environmental handicaps.

Still another object is to provide-a regulation circuit having a coarsecontrol feedback and a find. control feedback additively enabling a moreprecise output control.

BRIEF DESCRIPTION OF THE DRAWINGS 7 FIG. I shows a block diagram of thepreferred embodiment of the invention;

. FIG. 2 shows a schematic diagram of the FIG. 1 block diagram.

PREFERRED EMBODIMENT OF THE INVENTION Turning now to the drawings, theinvention permits the inclusion of a battery or similar power source Il. a series potential control 12 and a flood lamp 13 within a watertighthousing, not shownfor sake of simplicity,-without requiring outsidecontrol devices or remotely extending circuitry for regulating a preciselight intensity of the flood lamp. This regulation is achieved by theunique electrical interaction of a first feedback loop and a secondfeedback loop generally designated by the arrows and referencecharacters 14 and 15, respectively.

Loop 14 is responsible for the generation of a first feedback signal, acoarse feedback control signal, fed to the series voltage controlelement to regulate the control element's output voltage to a desiredlevel. Theloop includes a voltage sampler l6 bleeding off a portion ofthe output voltage and passing this sample to a comparator 17. A voltagestandard source 18 passes a signal having a desired voltage magnitude tothe comparator within which a comparison of the two voltages is made anda first control signal representative of the difference between thedesired voltage magnitude and the sample voltage is fed to an adder 2l.

Simultaneously, a radiation intensity sampler 19, here an opticalelectric-transducing photocell, samples the light intensity of lamp 13.A signal representative of the sampled radiated intensity is passed toan inverting amplifier 20 and the resultant signal, a second controlsignal, is passed to adder 21. These two control signals, added to forma composite signal,

are amplified in a feedback amplifier 22 and passed to a con trolcurrent adder 23. A current source 24, connected power source 11, passesan additive current to control current adder 23 to provide the properbiasing level within which the composite signal, when added to theadditive current, can effectively vary the impedance of the seriesvoltage control element voltage. I

The first loop is responsive to the output voltage of the controlelement to bring the output voltage to a desired potential establishedwithin the first feedback loop. In the second loop, however, the secondcontrol signal is generated from an optical-to-electrical conversionrepresentative of the lightlights intensity. Empirically, it has beendiscovered that irrespective of the factthat if the potential impressedacross a lamp is precisely regulated, the magnitude of light intensityis subject to fluctuation or diminishment caused by deterioration of thelamps reflective surfaces. This problem is especially prevalent in theinstant invention where the lamp is used in a corrosive environment.Therefore, the second feedback loop is necessary to preserve a constantlevel of light intensity by providing a second second control signalrepresentative of changing light intensity due to deterioration of thelamp. A hermetically sealed selenium photocell installed within thehousing provides the necessary degree of light intensity control.However, since such a photocell has a linear response over a limitedrange of light intensity, the output potential provided by the firstfeedback loop is of a magnitude that ensures the lamps operation withinthis limited range.

Looking now at the schematic diagram in FIG. 2, the boxed in phantom,having identical reference characters as shown in FIG. 1, contain theprincipal circuit elements. The output current of the series voltagecontrol is the sum of the current originating in current source 24 andthe feedback current originating in feedback loops l4 and 15. When theoutput voltage is greater than a desired voltage established by thevoltage standard source 18 or the light intensity is greater than adesired intensity determined by selective adjustment of a variableseries resistor 25, the negative feedback current from the two loopslowers the control current passed from current adder 23 to the bases ofparallel transistors 26 and 27 forming 'the series control elements. Thelowering of the total control current passed to the series voltagecontrol element lowers the output voltage impressed across lamp l3,schematically represented by a resistor. The voltage sampler l6,depicted as a potentiometer tapping off a portion of the series controlelements output voltage, passes the sample to a comparator junctionpoint designated by the numeral 17. A voltage standard source isestablished by a Zener diode having breakdown voltage equal to thedesired voltage and this magnitude of voltage is fed to the comparatorjunction. It is readily observed that an over voltage transferred by thevoltage sampler results in a negative feedback current being deliveredto the feedback amplifier and a consequent lowering of the total controlcurrent passed to the series voltage control element. The voltagesamplers transferring of an under voltage," with respect to the desiredvoltage as established by voltage standard source 18, results in alesser amount of feedback current to permit a greater total controlcurrent transfer to the control electrodes of the two power transistors26 and 27. Linear operation of the power transistors is ensured by thesupporting heat sink 29. I

The output current from the intensity sampler, a hermetically sealedselenium photocell 19, is fed to a common base transistor 30 presentinga low impedance load and to a second transistor 31 functioning as aninverting amplifier. The output signal produced by the interconnectedphotocell circuit is passed to an adder 21 for algebraic addition to thefirst signal originating in the first feedback loop and results in thetransfer of a composite signal to control current adder 23. Here, it

should be pointed out that the junction enclosed by the phantom boxdesignated both 17 and 21, performs the dual function of being a voltagecomparator 17 for the first feedback loop and as an adder 21 for thefirst control signal originating in the first feedback loop and thesecond control signal originating in the second feedback loop.

The -photocells constant monitoring of the flood lamp's radiatedintensity permits a feedback indicative of lamp deteriorationindependent of fluctuations in output voltage of the power source of orof the series voltage control element. Thus, independent, dual controlof the light intensity is simultaneously occurring to ensure a constantlight intensity output.

It is understood that the invention has been described without givingrepresentative values to circuit elements in FIG. 2. Given the values ofa particular power source and a desired light intensity, the choice ofcircuit components operatively duplicating the inventive concept setforth in the present disclosure, is well within the purview of oneskilled in the art and such changes and modifications may be madewithout departing from the scope of the invention as defined by appendedclaims.

lclaim:

1. An apparatus for controlling the light intensity of a lamp isolatedfrom external control comprising:

a storage battery slmilarly isolated fromexternal 'control;

an adjustable impedance including first and second power transistorsconnected in parallel with their respective collectors electricallyconnected to said storage battery and their emitters electricallyconnected to said lamp for transferring an output signal thereto;

a first feedback means including a Zener diode having a breakdownvoltage equal to a desired potential. a voltage sampler connected tosaid emitters bleeding off a portion of said output signal, and avoltage comparator coupled to said Zener diode and said voltage samplerfor comparing said desired potential with said portion to pass a firstsignal representative of their deviation to the bases of said first andsecond transistors to adjust said impedance for ensuring the transfer ofan output potential equal in magnitude to said desired potential; secondfeedback means including an internally carried photocell having a linearresponse over a limited range of light intensity to simultaneouslygenerate a linear second signal representative of light intensitydeviations from a desired light intensity caused by deterioration ofsaid lamp, electrically connected to said bases; and means for addingsaid first signal and said second signal to produce a composite signalelectrically connecting said bases to said first and second feedbackmeans for additively controlling said impedance to provide a lamppotential ensuring said desiredlight intensity.

2. An apparatus according to claim 1 further including: a

source of current deriving its power from said source of potential andinterposed between said adjustable impedance and

1. An apparatus for controlling the light intensity of a lamp isolatedfrom external control comprising: a storage battery similarly isolatedfrom external control; an adjustable impedance including first andsecond power transistors connected in parallel with their respectivecollectors electrically connected to said storage battery and theiremitters electrically connected to said lamp for transferring an outputsignal thereto; a first feedback means including a Zener diode having abreakdown voltage equal to a desired potential, a voltage samplerconnected to said emitters bleeding off a portion of said output signal,and a voltage comparator coupled to said Zener diode and said voltagesampler for comparing said desired potential with said portion to pass afirst signal representative of their deviation to the bases of saidfirst and second transistors to adjust said impedance for ensuring thetransfer of an output potential equal in magnitude to said desiredpotential; a second feedback means including an internally carriedphotocell having a linear response over a limited range of lightintensity to simultaneously generate a linear second signalrepresentative of light intensity deviations from a desired lightintensity caused by deterioration of said lamp, electrically connectedto said bases; and means for adding said first signal and said secondsignal to produce a composite signal electrically connecting said basesto said first and second feedback means for additively controlling saidimpedance to provide a lamp potential ensuring said desired lightintensity.
 2. An apparatus according to claim 1 further including: asource of current deriving its power from said source of potential andinterposed between said adjustable impedance and said first feedbackmeans and said second feedback means, said source of current producing acurrent additive to said composite signal for driving said control unit.